1. The Field of the Invention
The present invention generally relates to communication devices used within a communication system or network, and, more particularly, to a device for transceiving signals over multiple telephone lines or similar transceiving lines.
2. Present State of the Art
Throughout the ages man has initiated and developed numerous methods to communicate information. Communication in one form or another is used continuously, whether it be face to face conversation involving both body and verbal communication or through pictures, music, or art. With the advances in technology, however, individuals wish to spend more time communicating to discuss business, entertainment, and other daily events, but wish communication, in all its forms, to be more easily accomplished.
The modern society in almost every respect is crucially dependent on its ability to communicate signals or data, whether in digital or analog form, from one point to another. With the advances in technology the Internet has become ubiquitous for business and electronic commerce, education, entertainment, etc. As such, individuals, companies and other entities demand faster and faster communication speeds to manufacture, distribute and sell their products and services. In many situations, the speed of signal transmission or receiving (xe2x80x9ctransceivingxe2x80x9d) directly impacts the quality of the services provided via the Internet, for example real-time video conferencing requires a minimum transceiving speed to be feasible.
The communication channels over which data is transceived is almost always the widespread public switched telephone network (PSTN). The core of the PSTN in the United States and other industrialized countries is completely digital, while the connection to the digital backbone is traditionally analog. A digital connection to the PSTN is possible through a service such as the Integrated Services Digital Network (ISDN). The ISDN provides 2 digital channels that are each capable of transceiving signals or data at a rate of 64,000 bits per second (xe2x80x9cb/sxe2x80x9d) and a control channel that can transceive signals or data at 16,000 b/s.
To use the ISDN, a user""s central office (xe2x80x9cCOxe2x80x9d), such as a local telephone company""s switching office, must be upgraded to provide lines and other equipment capable of transceiving signals. Therefore, the user must replace the analog on-premises equipment with digital equivalents, while the individual lines at the CO must be modified to carry digital data such as fiber optic cable. The installation costs and monthly charges for connectivity through an ISDN are significant, such that most users do not have a digital connection to the PSTN. Furthermore, ISDN digital connections are infrequently offered in rural and sparsely populated areas since it is difficult for telephone companies to recoup their investment in equipment and installation. In light of this, most users continue to have an analog connection to their CO.
The analog portion of the PSTN was designed to carry voice as inexpensively as possible. In particular, most analog connections to a CO are bandlimited and carry signals with a bandwidth ranging from about 200 Hz to about 3200 Hz in the United States and from about 300 Hz to about 3400 Hz in some other countries. The band ranges were chosen decades ago, as the narrowest possible band which could contain specific important characteristics of the human voice. Any signals outside these ranges are typically sharply attenuated.
To transceive data over an analog connection to the CO requires a modem. A modem performs two tasks: modulation, which converts the digital signal into an analog signal in the upstream direction, and demodulation, which converts the analog signal into a digital signal in the downstream direction. Most modems today convert a digital data stream into an analog signal within the bandwidths referenced in regard to the PSTN.
In recent years substantial progress has been achieved in modem design. While earlier modems could operate only at rates of 2400 b/s, modem speeds have increased up to 33,600 b/s. See International Telecommunications Union, Telecommunication Standardization Sector (ITU-T) Recommendation V.34, Geneva, Switzerland (1994) which is hereby incorporated as a reference.
Unfortunately rates of up to 33,600 b/s are insufficient for many of the newer applications envisioned with the advent of the Internet, such as video conferencing. While text transmission is fast, facsimile and especially still image transmission is slow. Furthermore, even with current sophisticated audio compression algorithms only low-quality video and audio is possible.
There are fundamental limitations that reduce the quality of data transmission in addition to lowering the maximum achievable data rate over the PSTN. The capacity of a communication channel on the PSTN, as discussed in C. Shannon, xe2x80x9cA Mathematical Theory of Communication,xe2x80x9d Bell System Technical Journal volume 27, pp. 379-423 and pp. 623-656, 1948, which is incorporated herein by reference, is given by                     C        =                  W          ⁢                      xe2x80x83                    ⁢                      (                          1              +                              log                ⁢                                  xe2x80x83                                ⁢                                  S                  N                                                      )                                              (        1        )            
where C is the maximum achievable data rate in b/s, W is the bandwidth of the channel in Hertz, and S/N is the signal to noise ratio. For most of the PSTN of the United States S/N at present is below 2000 (approximately 30 dB). If we substitute these numbers into the above equation we can easily find out that C≈3000xc3x9712=36,000 b/s. Regardless of the sophistication of current signal processing algorithms or the speed of current processors, the maximum achievable data rate remains the same for a single PSTN line. It is clear that current modem standards have achieved a rate which is very close to the maximum possible. Thus the speed of modems is limited not by available technology, but by the limited bandwidth of the telephone system.
The bandwidth limitation becomes more acute when combined with the changing usage of the PSTN. In the past most of the traffic over the PSTN was voice, with very little percentage of the total traffic being data. At the beginning of the next century, however, the ratio of voice to data traffic is expected to become reversed; with more data traffic than voice traffic.
A significant portion of the increase data traffic is caused by the availability of the Internet access. Most users today connect to the Internet through their Internet Service Provider (xe2x80x9cISPxe2x80x9d). ISPs usually have a high-bandwidth direct digital connection to the PSTN. Normally high-rate of communication is necessary in one direction only, from the ISP to the user (the downstream direction). This arrangement allows speeds of up to 56,000 b/s in the downstream direction. Currently modems capable of receiving data at speeds up to 56,000 b/s are available from several modem vendors, such as the 3Com Corporation, Santa Clara, Calif.
Many 56,000 b/s modems are capable of transceiving signals at various rates. Furthermore, the ITU-T V.90 standard for modems that can operate at rates up to 56,000 b/s actually envisions several possible modem data rates that vary based on the telephone line conditions, such as the effects of signal-to-noise ratio. Thus, unlike previous modem standards ITU-TV.90 does not specify a single data rate in the downstream direction. The allowed rates in the downstream direction range from about 28,000 to 56,000 in 1,333 b/s increments.
In normal communication sessions, two modems that are in communication will evaluate the telephone line conditions according to a line probing technique. Such line probing techniques are discussed for example in U.S. Pat. No. 5,515,398 entitled xe2x80x9cModem line probing signal techniques,xe2x80x9d issued to Walsh et al. which is assigned to the assignee of the present invention. The superior the line conditions, the higher the data rate at which the two modems will choose to operate.
Line characteristics of the PSTN lines can change with time, however, and may be varied through influence of electric and magnetic fields that are in close proximity to the PSTN lines. For example, power lines can induce a 60 Hz hum onto an analog telephone line. Furthermore, unwanted signals from adjacent telephone lines can induce unwanted voltages, called crosswalk. The influence of hum and crosswalk decrease the signal-to-noise ratio (S/N) and reduce the maximum data rate that can be achieved over the telephone line. Each time the line characteristics deteriorate the modems in communication negotiate to select a lower rate at which to communicate reliably. If the line characteristics improve the modems will select a higher rate. Therefore, over a single telephone line it is possible to connect sometimes at 49,333 b/s, while at another time is only possible to achieve 45,333 b/s.
Unlike end-to-end digital connections used by an ISP, the analog telephone lines making up the PSTN are widely available and relatively much more expensive. An increasing number of businesses and people have two and more telephone lines to allow them to perform multiple tasks concurrently. Indeed many user add a second telephone line just for occasional use, for example, for facsimile services. The precious bandwidth that is offered by the second telephone line is wasted most of time. The productivity of many users would be increased if they could use the second telephone line to achieve higher-speed access to an ISP, other modems, or the like.
Unfortunately, there are numerous problems with forming a modem that is capable of communicating signals over two or more telephone lines. A significant problem is the variability of telephone line conditions and characteristics.
When two modems operate over two or more telephone lines, if the line conditions on all lines are identical, then clearly the aggregate data rate is the sum of the data rates that are achieved over the individual phone lines.
However, the line conditions, will not always be identical. As a matter of fact, they are very likely to be different. For example, it is clear that the amount of noise induced onto two telephone lines will be different. This noise typically comes from neighboring telephone lines, power lines, etc, as stated above. According to the Shannon""s limit the maximum data rates that can be achieved over the two lines will be different, as the maximum achievable data rate over each line will directly depend on the signal-to-noise ratio (SIN) over that line. If the rates are different, however, it is not obvious how can we achieve an aggregate data stream equal to the sum of the data rates achieved over the individual lines. One obvious possibility is to select the lowest data rate that the telephone lines can work at and use this rate on all telephone lines. For example, if it is found that one of the lines supports 49,333 b/s and the other supports 45,333 b/s, assuming that we have two telephone lines, we might select to operate at 45,333 b/s over the two telephone lines, achieving an aggregate data stream of 90,666 b/s. Clearly this is not the optimum solution. It is very desirable to achieve a data rate of 94,666 b/s, which is the sum of the two data rates in this example.
Thus, the present state of the art dictates that if the two or more data rates achievable over the different telephone lines are not the same negotiation is performed, followed by a fallback on all lines onto a data rate equal to the rate achieved by the slowest line. It is clear that the aggregate data rate would be only the data rate achieved on the slowest line times the number of channels, but not the sum of the maximum data rates on every line. Furthermore the process of negotiating different rates on the lines is slow. It is also very inefficient to require the modems to negotiate new communication rates each time the minimum data rate changes.
These disadvantages can have a significant and negative effect on a modem""s performance and might make it less commercially viable for sale.
It is an object of the present invention to provide a communication device that is capable of transceiving signals along two or more communication lines.
It is another object of the present invention to provide a communication device that is capable of transceiving data at a rate corresponding to the maximum aggregate communication rate of two or more communication lines.
Another object of the present invention is to provide a communication device that achieves an aggregate data rate that is the sum of the maximum data rates achievable on the individual telephone lines.
It is another object of the present invention to provide a communication device that is cheap and inexpensive.
Still yet another object of the present invention is to provide a communication device that is capable of secure communication over an unsecured communication network.
Yet another object of the present invention is to provide a communication device that is capable of multiplexing signals along multiple telephone lines at a communication rate substantially similar to the aggregate communication rate of the multiple telephone lines.
It is another object of the present invention to provide a method of manipulating signals to be communicated along multiple telephone lines into a form that allow maximization of the communication rate of the telephone lines.
It is another object of the present invention to provide a method and system that achieves signal communication rates that are substantially equal to the aggregate of the telephone lines used.
Still yet another object of the present invention is to provide a modem device that is capable of secure communication over an unsecured communication channel.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a communication system configured to transceive a signal along multiple communication media of the communication system to thereby increase the rate at which the signal is transceived is disclosed. The communication system comprising a source configured to transceive a signal. A communication apparatus configured for decomposing the signal into a plurality of manipulated signals. The number of the plurality of manipulated signals being determined by the number of the multiple communication media in communication with the source and the maximum transceival rate of each communication media. In communication with the communication apparatus is a reconstructing apparatus that is configured for reconstructing the plurality of manipulated signals into the signal, the signal being capable of being transceived by a host.
In general, the present invention allows a users to reap maximum benefits of a xe2x80x9cbandwidth-on-demandxe2x80x9d policy where users can access any type of digital signal (high-quality audio, video, etc.) at speeds which are maximum for their available telephone lines. By allowing increase signal transceival rates, the present invention makes several new applications possible, such as for example videophone, teleconferencing, high-quality video and audio, etc.